The Descent of Man

cover, hardly any foreign species, differ much
in colour according to sex; though this is the
case with many brilliant butterflies. The male,
however, of one American moth, the Saturnia
Io, is described as having its fore-wings deep
yellow, curiously marked with purplish-red
spots; whilst the wings of the female are purple-brown,
marked with grey lines. (19. Harris,
'Treatise,' etc., edited by Flint, 1862, p. 395.) The
British moths which differ sexually in colour
are all brown, or of various dull yellow tints, or
nearly white. In several species the males are
much darker than the females (20. For instance,
I observe in my son's cabinet that the males are
darker than the females in the Lasiocampa
quercus, Odonestis potatoria, Hypogymna dispar,
Dasychira pudibunda, and Cycnia mendica.
In this latter species the difference in colour
between the two sexes is strongly marked; and
Mr. Wallace informs me that we here have, as
he believes, an instance of protective mimicry
confined to one sex, as will hereafter be more